The invention relates to a piston and cylinder unit having a valve which serves to regulate the piston speed and has an open position in which it allows free flow of driving fluid to the piston and a choking position in which it chokes the flow of the driving fluid in order to influence the piston speed, the regulating valve further being connected with at least one sensor responding to a given piston setting and then changing the valve setting.
Such piston and cylinder units are employed to change the speed of the moving piston in a way dependent on its instantaneous position. Fields of application are for instance in connection with buffering the end of the piston stroke when approaching its terminal position, as for example in robots and materials handling equipment. The operation of the regulating valve controlling the supply of fluid to the cylinder and therefore at the same time changing the speed of the piston takes place mechanically using a cam follower or similar sensing member on the valve member to sense a cam rail, on which the follower runs. In accordance with the geometry of the cam rail, the regulating valve is opened to a greater or lesser extent. A disadvantage in the case of such a design of piston and cylinder unit is that it takes up a large amount of space, since the regulating valve has to be located right on the cylinder or in the direct vicinity thereof. Equipment having to be fitted with a large number of such piston and cylinder units as for example industrial robots is therefore so bulky that its applications become very limited. Furthermore, such a mechanical following mechanism has a high wear rate and the length of life of the cylinder is seriously limited by the irregular loading on the piston rod when the regulating valve is actuated. In particular, the bushings or the like on which the piston rod runs in the cylinder are heavily loaded so that the piston rod may run skew and then seize up.